/**
 * [monthSize 获得指定日期所在月的天数]
 * @param  {[Date]} oDate [指定的日期，非必填，默认为当天]
 * @return {[Int]}       [总天数]
 */
function monthSize(oDate) {
    oDate = oDate ? oDate : new Date();
    let year = oDate.getFullYear(),
        month = oDate.getMonth(),
        _oDate = new Date();
    _oDate.setFullYear(year);
    _oDate.setMonth(month + 1, 0);
    return _oDate.getDate();
}
